1. Field of the Invention
This application relates to a system and method for producing steam for Enhanced Oil Recovery (EOR) facilities. This invention relates to processes for producing steam in a commercially available steam generation facility from carbon or hydrocarbon fuel and any water source, possibly with high levels of solids and organics, without liquid waste discharge.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98
The invention includes an atmospheric or pressurized solid fuel boiler package, OTSG (Once Through Steam Generator) unit or any other commercial available steam generator unit. The BFW (Boiler Feed Water) water for the commercially available steam generation facility is produced using a commercially available water treatment plant. This system can be based on distillation technology. The distillation technology used can be any commercially available water distillation unit like a Single Effect Distiller, Multi Effect Distillation (MED), Single or Multi-Stage Flash (MSF), or, Mechanical Vapor Compression (MVC). Other commercially available water treatment methods, like lime softeners, or cation-anion reactors, can also be used. The treated water is used by the steam generation facility to generate pure steam (without combustion gases) for injection into an underground formation to recover heavy crude oil. The rejected liquids from the water treatment facility (like brine, lime sludge, filter back-wash etc.) and oil contaminated water from the water-oil separation facility are used by a DCSG (Direct Contact Steam Generation) to generate gas (steam and combustion gas) and a solid waste discharge. The water and the heat recovered from the DCSG discharged gas flow are pressurized, at pressures greater then 103 kpa, and used in the water treatment facility, like in thermal distillation facilities, or for BFW heating for steam generation.
The injection of steam into heavy oil formations was proven to be an effective method for EOR and it is the only method currently used commercially for recovery of bitumen from deep underground oilsand formations in Canada. It is known that EOR can be achieved where combustion gases, mainly CO2, are injected into the formation, possibly with the use of DCSG as described in my previous applications. The problem is that oil producers are reluctant to implement significant changes to their facilities, especially if they include changing the composition of the injected gas to the underground formation and the risk of corrosion in the carbon steel pipes due to the presence of the CO2. That problem is solved in this application with the use of commercially available steam generation and water treatment facilities together with the DCSG, and maintains most of the advantages of the DCSG for the overall process in the integrated system as described herein.
By integrating a commercially available boiler, a commercially available distillation facility, and DCSG with an enhanced oil recovery unit, as described in this application, the water and combustion gas are separated with Zero Liquid Discharge (ZLD). A ZLD facility is more environmentally friendly compared to a system that generates reject water and sludge. In one embodiment, most of the water vapor and heat is recovered and used to generate distilled water for additional steam production. The system might also include a direct contact brine evaporator dryer (similar to DCSG), a dry solids removal system (to remove solids from the gas stream), and a wet steam generator (a scrubbing vessel for scrubbing solids, sulfur and generating saturated wet steam). In one embodiment of the current invention, the boiler can be a Pressurized low efficiency boiler (without economizer) as the heat of the discharged combustion gas is used in the direct contact dryer and in the direct contact wash vessel to evaporate water by direct contact with the boiler combustion gas. The brine from the distillation facility can be recycled to the direct contact liquid evaporator and dryer where additional steam is generated and dry solid wastes will be removed from the product gas in a commercially available gas-solid separation unit.
The use of a crystallizer to further concentrate the brine and a direct-fired dryer (typically operated with natural gas) to treat the concentrated discharge from the crystallizer is a known prior art. One of the problems is that most of the energy and the water generated are wasted. As a result, the CO2 emissions for a prior art ZLD system will be higher when compared to a similar system with liquid discharge, to deep disposal wells, as an example. In the present invention, the DCSG generates a pressurized high temperature flow where the energy, including the evaporation/condensation energy, is recovered while most of the steam is condensed and recovered as liquid water. The overall thermal efficiency depends on the system pressure (as well as on other factors)—for higher pressures, the temperatures and the thermal efficiency will increase. (see examples 1 and 2) The downside of higher pressures is the increased cost of the facility (both to construct and to operate). The operating pressure for the system will be dictated by evaluating the efficiency in comparison to the TIC (Total Installed Cost) and the operating cost.
The definition of “Direct Contact Steam Generation” (DCSG) is that the heat is transferred between the liquid water and the combustion gas. This is accomplished through the direct mixing of the two flows (the water and the combustion gases). In the DCSG, the combustion pressure is similar to the produced steam pressure and the combustion gases are mixed with the steam. (See FIG. 20 for the schematic of the Direct and Non-Direct steam generation methods)
In a Non-Direct Steam Generator (like a steam boiler with a steam drum and a mud drum) or “Once Through Steam Generator” (OTSG), the heat transfer and combustion gases are not mixed and the heat transfer is done through a wall (typically a metal wall), where the pressure of the generated steam is higher than the pressure of the combustion. This allows for the use of atmospheric combustion pressure. The product is pure steam (or a steam and water mixture, as in the case of the OTSG) without combustion gases. A direct and indirect steam generator can be integrated into one unit as described, for example, in the down-flow boiler described in FIG. 5 and in the fluidized bed boiler described in FIG. 15 where a portion of the combustion heat is used for generating high pressure steam from di-mineralized treated water through the metal walls (usually tube type) of the heat exchanger, where the rest of the heat is used for generating steam from low quality water (such as water that may include high levels of solids, organics and hydrocarbons) through direct contact with the combustion gas.
There are patents and disclosures issued in the field of the present invention. U.S. Pat. No. 6,536,523 issued to Kresnyak et al. on Mar. 25, 2003 describes the use of the blow-down heat as the heat source for water distillation of de-oiled produced water in a single stage MVC water distillation unit. The concentrated blow-down from the distillation unit can be treated in a crystallizer to generate solid waste.
U.S. Pat. No. 6,733,636 issued to Heins on May 11, 2004 describes a produced water treatment process with a vertical MVC evaporator.
Paper 2005-115 introduced at the 2005 Canadian International Petroleum Conference named: “World First SAGD facility Using Evaporators, Drum Boilers, and Zero Liquid Discharge Crystallizer to treat Produced Water” by Heins et al, describes the integration of vertical MVC and crystallizer to generate BFW (Boiler Feed Water).
A CHOA (Canadian Heavy Oil Association) presentation by Gary Giesbrecht from Petro-Canada on Feb. 13, 2007 described the Zero Liquid Discharge at Mackay River that includes evaporators, steam drive crystallizer and air-cooled condensers.
Canadian patent application 2,547,503, filed Jun. 16, 2005 by Minnich et al, describes the use of a high pressure and high temperature distillation unit combined with a steam boiler for the production of steam for injection into a SAGD injection well.
U.S. Pat. No. 7,578,354 issued to Minnich et al. on Aug. 25, 2009 describes the use of MED for generating steam for injecting into an underground formation. U.S. Pat. No. 7,591,311 issued to Minnich et al. on Sep. 22, 2009 describes evaporating water to produce distilled water and brine discharge, feeding the distilled water to a boiler, and injecting the boiler blow-down water from the boiler to the produced steam. The solids and possibly volatile organic remains are carried with the steam to the underground oil formation. The concentrated brine is discharged in liquid form.
Canadian patent application 2609419 filed on Nov. 2, 2007 by Speirs et al. describes a method to recover heat and water from tailing water by using inert gas. The tailing water heat energy is used for evaporation. The water vapor behaves according to its partial pressure with the inert gas, resulting in low condensation temperatures at the low pressures.
Canadian patent application 2609859 filed on Nov. 2, 2007 by Speirs et al. describes a method to recover heat and water from hot tailing water discharged from downstream oil production facilities by using vacuumed MED or MSF to generate distilled Boiler Feed Water quality from waste heat of the tailing water.
Canadian patent application 2610052 filed on Nov. 8, 2007 by Speirs et al. describes a method to recover heat, energy and water from the hot tailing water discharged from downstream oil production facilities. The recovery process is using MSF process. Due to the low temperature of the feed water there is a need for a strong vacuum and especially a very cool condensing side. In this application, the process is driven by the temperature differences occurring between different process flows in an oil-sand plant where the inlet cold water flow is used as a heat sink to condense the low pressure steam. There are problems with the general approach of recovering heat and distilled water from tailing water. The tailing water is generally at a low temperature that requires the use of a strong vacuum and low condensing temperature for recovered distilled water. Due to the low levels of energy only small portion of the water can be recovered. Another significant problem is the high levels of abrasive solids content and the other impurities in the source as other contaminates (like hydrocarbon traces). This can make the use of heat exchanger and other equipment impractical. In my application the solids are removed in solid form from the steam during or after the combustion or the DCSG.
This invention's method and system for producing steam for extraction of heavy bitumen includes the steps of mixing fuel with an oxidizing gas; combustion of the mixture and possibly capturing a portion of the combustion heat for generating steam from clean, de-mineralized water (BFW). Then, mixing the combustion gas with low quality contaminated water and transferring the liquid water to gas phase with solids, wherein solids are separated from the gas phase. The gas phase is mixed with saturated water to scrub the remaining solids and produce saturated steam. The solid rich saturated water is recycled back and mixed with the combustion gases for liquid gasification. The saturated steam is condensed to generate heat and clean condensed water for steam generation. The heat can be used for evaporating additional low quality water at the distillation facility to produce distilled water and concentrate brine. The brine is recycled back for liquid gasification. The high pressure steam is sent to an enhanced oil recovery facility and injected into an injection well for extraction of heavy oil.
The above-mentioned invention also relates to processes for making SAGD and CSS (Cyclic Steam Stimulation) facilities, or other EOR facilities, more environmentally friendly by using low quality fuels, like petcoke or coal, instead of natural gas. It reduces the amount of greenhouse gas emissions through increased thermal efficiency. The generated CO2 gas can be recovered for underground sequestration or for usage in EOR.
Steam injection into deep underground formations has proven to be an effective method for EOR facilities producing heavy oil from an oil-sand formation. It is typically done through SAGD, Steam Drive or by CSS. In recent years, the SAGD method has become more popular, especially for heavy oil sand formations. Presently, different forms of steam injection (sometimes with hydrocarbons) are the only method commercially used on a large scale for recovering oil from deep oil sands formations.
The use of DCSG (Direct Contact Steam Generator) to generate high pressure steam and flue gas mixture has many advantages; however it might have some significant disadvantages resulting from the presence of the combustion gases, mainly CO2, within the steam. That might present a problematic situation when used in combination with particular types of underground formations and recovery processes.
It is a goal of the present invention to provide a system and method for the improvement of EOR facilities like SAGD, through a supply of high-pressure steam for underground injection wells.
Another objective of the present invention is to provide a system that can produce steam from distilled water and the brine produced by the distillation facility without liquid discharge.
Another objective of the invention is to provide a system and method that utilizes low-grade fuel with commercially available solid fuel burner packages.
An additional objective of the present invention is to provide a system and method that will remove produced solids from the system by converting the liquids to gas phase and removing solids from the gas phase. The solids are a product of the fuel and the evaporated water. The solids can be silicon based materials, calcium based materials, different type of salts carried by the water, etc.
Furthermore, it is another objective of the present invention to provide a system and method that enhances thermal efficiency and minimizes the amount of energy used to produce the steam injected into the underground formation to recover heavy oil.
It is a further objective of the present invention to provide a system and method that minimizes the amount of greenhouse gases released into the atmosphere.
A further objective of the present invention is to provide a system and method that serves to make EOR facilities, like SAGD, more environmentally friendly by using low-quality fuel like petcoke or coal.
It is still a further objective of the present invention to provide a method for steam production for the extraction of heavy bitumen.
It is an objective of the present invention to provide a method for producing super-heated, dry, solid-free steam.
It is still a further objective of the present invention to provide a method that uses discarded water, possibly mixed with oil, clay or silica sand from a SAGD facility.
It is another objective of the present invention to provide a system for oil recovery using heat injection.
These and other objectives and advantages of the present invention will become apparent from a reading of the attached specifications and appended claims.